This invention relates to photographic lenses and more particularly to telephoto lenses.
The present inventor has proposed a practical example of a telephoto lens having focusing provision made at a part of the rear lens group in U.S. Pat. No. 4,045,128. The design features of this lens are, however, because of their adaptation to a comparatively long focal length with a narrow image angle, found to lead to large deviations of aberrations, namely, distortion, astigmatism, coma, and chromatic variation of astigmatism or of coma throughout the focusing range when applied to a lens system with the same arrangement of the components but having a shorter focal lenght, since the other part of the rear group which remains stationary during focusing can not contribute to a good compensation for the residual of aberrations introduced by the forwardly located lens components. As the angular field coverage is increased, therefore, the amount of positive distortion left uncorrected at the image is increased to an unacceptable level. This is also true in the state of correction of spherical aberration.